The invention relates to apparatus for the treatment of water, particularly stormwater, to reduce levels of contaminants such as garbage, sediment, heavy metals, oils and greases, organic toxins, and the like. Specifically, the invention provides a modular filter assembly that incorporates a regulated surface cleaning mechanism that is capable of using a wide variety of filtration materials to provide various levels of stormwater treatment.
Stormwater is pure rainwater plus any particulate debris and dissolved materials that the rainwater carries along with it. In urban areas, rain that falls on the roofs of houses, collects on paved areas like driveways, roads and sidewalks is typically diverted through a system of pipes that is separate from the sewerage system. Unlike sewage, stormwater is not treated, but flows directly from streets and gutters into rivers, lakes and the ocean.
Stormwater can therefore be a form of diffuse or non-point source pollution. It can entrain pollutants, such as garbage, sediment, organic matter, heavy metals, and organic toxins, and flush them into receiving water bodies. As a consequence, natural bodies of water that receive stormwater may also receive pollutants capable of irreparable environmental harm.
The amount of stormwater pollution entering into such receiving bodies of water is related to the degree of urbanization in the surrounding area and the nature of the surrounding activities. Urbanization results in the covering of land with low-permeability structures, such as roadways, parking lots, and rooftops, which both generate large volumes of stormwater and accumulate pollutants. Since these types of surfaces do not allow rainfall to infiltrate, they allow the accumulated pollutants to be washed into stormwater drainage systems.
Prior to extensive human modification of the natural landscape, contaminated stormwater was not a significant problem. Rain fell on porous, natural surfaces where gradual percolation through the earth provided natural filtration before stormwater entered aquifers, streams, lakes, bays, and other natural water bodies. In addition, erosion due to excessive stormwater volumes was minimal and contaminants such as garbage, oil and grease, heavy metals, and organic chemicals were insignificant. In today""s largely urban and industrial world, stormwater is a significant source of aquatic pollution.
In an effort to address the environmental problems posed by polluted stormwater, traps and filters for stormwater have been developed. U.S. Pat. No. 5,322,629 (hereby incorporated by reference) describes a method and apparatus for treatment of stormwater by vertical filtration through a bed of high-quality leaf compost material that removes pollutants prior to discharge into a receiving water body.
A granular form of compost that improves the overall performance of such filtration systems was described in U.S. Pat. No. 5,624,576 (hereby incorporated by reference). The permeability of a filter containing such granular compost is increased, and can be maintained for an extended period of time.
Extended filter permeability can be achieved by orienting the surface of the media bed vertically rather than horizontally, as described in U.S. Pat. No. 5,707,527 (hereby incorporated by reference). Vertical filter beds discourage the collection and storage of settled solids on the surface of the filter, which otherwise typically leads to xe2x80x9cblindingxe2x80x9d or surface loading, a rapid clogging of the outer surface of the filter. The use of a vertical filtration surface also facilitates the maintenance of the system both by keeping the bulk of the captured solids off of the media surface and by forcing the enclosure of the media into more manageable, engineered structures.
The improved filter apparatus described in U.S. Pat. No. 6,027,639 (hereby incorporated by reference) features a siphon-inducing mechanism and is somewhat xe2x80x9cself-cleaningxe2x80x9d, thereby improving the operational life of the media bed. The filter apparatus of the ""639 patent utilized a sealed upper housing that included a check valve for air evacuation within the housing. An induced siphon effect pulled stormwater through the filter until air was pulled through an air inlet along the lower perimeter of the housing, disrupting the siphon. It was intended that the air stream that resulted from such a siphon-breaking event would produce turbulence and thereby clean the filter. In particular, the filter apparatus of the ""639 patent utilized a fabric filtration medium around the outside of the media bed to prevent particulates from clogging the media bed, and the periodic turbulence was intended to keep the fabric filter free of clogging particulates.
Unfortunately, although the filter basket of the ""639 patent was an improvement over existing stormwater filter systems, it nevertheless possessed some shortcomings. The filter assembly typically featured a flush, circumferential air inlet along the lower perimeter of the filter housing. It was intended that the air stream resulting from the siphon-breaking event would be evenly distributed along the surface of the filter, producing turbulence and thereby cleaning the filter. In actual practice, however, the filter basket can only rarely be installed with perfectly horizontal alignment, and the air streams that result upon breaking the siphon are therefore typically concentrated along a single highest portion of the lower perimeter of the filter housing, and are highly localized at a single portion of the fabric filtration medium. The resulting localized air stream results in the cleaning of only a single section of the fabric filter medium, rather than the entire filter surface. Generally, these quick, uncontrolled, localized regions of turbulence typical of the previously described filter assemblies clean the outer surface of the filter less effectively than would a more prolonged and evenly distributed region of turbulence.
In addition, it was found that fabric filter media often suffered from rapid clogging. Filtered particulate matter could create rapid and persistent surface loading of the fabric filter, which was then exaggerated by the effects of a poorly functioning cleaning mechanism.
What is needed is a stormwater filter apparatus that 1) does not require the attachment or use of additional parts or material; 2) does not contribute additional mechanical complexity to the filter basket apparatus; 3) permits the induced siphon effect to be broken in a regulated and more distributed fashion that spreads the turbulent, scouring air stream along a greater portion of the outer surface of the filter medium; and/or 4) that can maintain high surface permeability while retaining large volumes of particulate matter before filtration capacity is significantly diminished.
The invention provides a filter assembly that includes a hood that incorporates a plurality of voids arranged in a horizontally-aligned array, a drain manifold, a filter medium between the hood and the drain manifold, a drainage space that is in fluid communication with both the filter medium and the drain manifold, a check valve in the hood that permits air to escape, but does not permit air to enter the drainage space, and a drain valve assembly that permits a first rate of fluid flow from the drainage space to the drain manifold until the drainage space fills with fluid to a specified depth, whereupon the drain valve assembly permits a second increased rate of fluid flow to the drain manifold. This second rate of fluid flow from the drainage space, acting in combination with the one-way check valve creates a siphon effect that draws additional fluid through the filter medium and out the drain manifold. This induced siphon effect continues until air is drawn under the hood through the plurality of voids, disrupting the siphon and restoring the first rate of fluid flow through the filter medium.
In one aspect of the invention, the filter assembly includes a cylindrical hood with a horizontally-aligned array of voids near the lower edge of the hood, a cylindrical drainage space placed concentrically within the hood, an annular water filtration medium between the hood and the drainage space that is in fluid communication with the drainage space, and a check valve in the hood that permits air to escape the filter assembly in response to rising stormwater within the hood but prevents air from entering the filter assembly.
The filter assemblies of the invention provide a float-actuated, siphonic, filter cartridge with a regulated surface cleaning mechanism for the filtration of water, particularly stormwater, before it is discharged. The design of the assembly of the invention facilitates the use of various filter mediums, offering flexibility in targeting a wide spectrum of pollutants. The regulated surface cleaning feature of the filter assembly effectively prevents surface loading of a majority of the outer filter surface, resulting in extended periods of useful service with minimal maintenance and without requiring an additional fabric filtration medium.
The advantages of the present invention will be understood more readily after a consideration of the drawings and the Detailed Description.